Methods and apparatuses for reducing heat loss from edge directors

ABSTRACT

An apparatus and methods for making a glass ribbon includes a forming wedge with a pair of inclined forming surface portions converging along a downstream direction to form a root. The apparatus further includes an edge director intersecting with at least one of the pair of downwardly inclined forming surface portions, and a replaceable heating cartridge configured to direct heat to the edge director and thermally shield the edge director from heat loss. A replaceable heating cartridge is also provided for directing heat to the edge director and thermally shielding the edge director from heat loss.

This is a divisional of U.S. patent application Ser. No. 14/278,582filed on May 15, 2014, the content of which is incorporated herein byreference in its entirety.

BACKGROUND Field

The present specification generally relates to apparatuses and methodsfor making glass ribbons, and more specifically, to apparatuses andmethods for making glass ribbons with edge directors and replaceableheating cartridges that direct heat to the edge directors and thermallyshield the edge directors from a plurality of edge rollers.

Technical Background

Glass forming apparatuses are commonly used to form various glassproducts such as glass sheets used for LCD displays and the like. Theseglass sheets may be manufactured by downwardly flowing molten glass overa forming wedge to form a continuous glass ribbon. Edge directors arefrequently provided at opposed ends of the forming wedge to help achievea desired glass ribbon width and edge characteristics. However, theseedge directors may also act as heat sinks leading to the devitrificationof molten glass in proximity to the edge directors. Such devitrificationmay cause defects in the glass ribbon which, in turn, may lead tomanufacturing losses and increased production costs.

Accordingly, a need exists for alternative methods and systems forforming glass ribbons which mitigate devitrification of the glassproximate to the edge directors.

SUMMARY

According to one embodiment, an apparatus for making a glass ribbon withreduced devitrification is provided. The apparatus may include a formingwedge with a pair of inclined forming surface portions converging alonga downstream direction to form a root. The apparatus further includes anedge director intersecting with at least one of the pair of downwardlyinclined forming surface portions, and a plurality of edge rollerspositioned downstream from the root and edge director. The plurality ofedge rollers may be positioned to engage an edge portion of the glassribbon. A housing may enclose the forming wedge, edge director, and theplurality of rollers. The apparatus may further include a removableheating cartridge that is positioned in a port of the housing below theedge director. The heating cartridge may include an enclosure having aheat directing surface that is inclined at an angle of less than about90° with respect to a bottom surface of the enclosure. The heatdirecting surface may include at least one heating element positioned onor adjacent to a face thereof. The heating cartridge may be orientedsuch that the heat directing surface faces the edge director, a viewfactor from the heat directing surface is greater at the edge directorthan at the edge rollers, and the lower edge of the heat directingsurface and the bottom surface of the heating cartridge are at leastpartially positioned between the edge director and the plurality of edgerollers to thermally shield the edge director from the plurality of edgerollers.

In another embodiment, a replaceable heating cartridge for use in anapparatus for making a glass ribbon with reduced devitrification isprovided. The replaceable heating cartridge may include an enclosurehaving a heat directing surface that is inclined at an angle of lessthan about 90° with respect to a bottom surface of the enclosure. Theheat directing surface may include at least one heating elementpositioned on or adjacent to a face thereof. The cartridge may furtherinclude refractory material disposed within the enclosure behind theheat directing surface. A view factor from the heat directing surfacemay be greater above the bottom surface of the enclosure than below thebottom surface of the enclosure, and the lower edge of the heatdirecting surface and the bottom surface of the heating cartridge maythermally shield the area above the heat directing surface from the areabelow the heat directing surface.

In yet another embodiment, a fusion draw method of making a glass ribbonwith reduced devitrification may include flowing molten glass over apair of downwardly inclined forming surface portions of a forming wedge,the downwardly inclined forming surface portions converging along adownstream direction to form a root. The method may further includeflowing the molten glass over an edge director intersecting with atleast one of the pair of downwardly inclined forming surface portions,drawing the molten glass from the root of the forming wedge to form theglass ribbon, and engaging an edge portion of the glass ribbon with aplurality of edge rollers positioned downstream from the root and edgedirector. The method may further include heating the edge director witha replaceable heating cartridge located in a port in the housing. Thereplaceable heating cartridge may be positioned between the plurality ofedge rollers and the edge director. The replaceable heating cartridgemay include an enclosure having a heat directing surface that isinclined at an angle of less than about 90° with respect to a bottomsurface of the enclosure. The heat directing surface may include atleast one heating element positioned on or adjacent to a face thereof.The replaceable heating cartridge may be oriented such that the heatdirecting surface faces the edge director, a view factor from the heatdirecting surface is greater at the edge director than at the edgerollers, and the lower edge of the heat directing surface and the bottomsurface of the replaceable heating cartridge are at least partiallydisposed between the edge director and the plurality of edge rollers tothermally shield the edge director from the plurality of edge rollers.

Additional features and advantages of the apparatus and methods formaking a glass ribbon and replaceable heating cartridge for use in suchapparatus and methods will be set forth in the detailed descriptionwhich follows, and in part will be readily apparent to those skilled inthe art from that description or recognized by practicing theembodiments described herein, including the detailed description whichfollows the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description describe various embodiments and areintended to provide an overview or framework for understanding thenature and character of the claimed subject matter. The accompanyingdrawings are included to provide a further understanding of the variousembodiments, and are incorporated into and constitute a part of thisspecification. The drawings illustrate the various embodiments describedherein, ad together with the description serve to explain the principlesand operations of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts an apparatus for making glass according toone or more embodiments shown and described herein;

FIG. 2 schematically depicts an apparatus for making glass according toone or more embodiments shown and described herein which comprises across sectional perspective view of the embodiment along line 2-2 ofFIG. 1;

FIG. 3 schematically depicts a side view of the apparatus for makingglass of FIG. 2 according to one or more embodiments shown and describedherein;

FIG. 4A schematically depicts a replaceable heating cartridge for use inan apparatus for making glass according to one or more embodiments shownand described herein and FIG. 4B schematically depicts a cross sectionof the replaceable heating cartridge along line 4-4 of FIG. 4A;

FIG. 5 schematically depicts a perspective back view of the replaceableheating cartridge for use in the apparatus for making glass of FIG. 4according to one or more embodiments shown and described herein;

FIG. 6 schematically depicts a replaceable heating cartridge for use inan apparatus for making glass according to one or more embodiments shownand described herein. The heating element is not shown in this design;and

FIG. 7 schematically depicts the increased edge director temperaturewith the use of the replaceable heating cartridge with an inclined angleα of the heat directing surface of about 60° relative to the bottomsurface compared to a heating cartridge with an inclined angle α of theheat directing surface of 90° relative to the bottom surface.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of the apparatusesand methods for making glass ribbon and replaceable heating cartridgesfor use in such apparatuses and methods, examples of which areillustrated in the accompanying drawings. Whenever possible, the samereference numerals are used throughout the drawings to refer to the sameor like parts. One embodiment of an apparatus for making glass is shownin FIG. 1, and is designated generally throughout by the referencenumber 10. The apparatus generally includes a heating cartridge that isremovably positioned in a port of a housing surrounding a forming vesselbelow an edge director affixed to the forming vessel. The heatingcartridge may comprise an enclosure having a heat directing surface thatis inclined at an angle of less than about 90° with respect to a bottomsurface of the enclosure. The heat directing surface includes at leastone heating element positioned on or adjacent to a face thereof. Theheating cartridge is oriented such that the heat directing surface facesthe edge director and a view factor from the heat directing surface isgreater at the edge director than at edge rollers located below the edgedirector. The lower edge of the heat directing surface and the bottomsurface of the heating cartridge are at least partially positionedbetween the edge director and the edge rollers to thermally shield theedge director from the plurality of edge rollers. Apparatuses for makingglass and replaceable heating cartridges for use in such apparatuseswill be described in further detail herein with specific reference tothe appended drawings.

Referring now to FIG. 1, one embodiment of a glass forming apparatus 10for making glass, such as a glass ribbon 12, is schematically depicted.The glass forming apparatus 10 generally includes a melting vessel 15configured to receive batch material 16 from a storage bin 18. The batchmaterial 16 can be introduced to the melting vessel 15 by a batchdelivery device 20 powered by a motor 22. An optional controller 24 maybe provided to activate the motor 22 and a molten glass level probe 28can be used to measure the glass melt level within a standpipe 30 andcommunicate the measured information to the controller 24.

The glass forming apparatus 10 can also include a fining vessel 38, suchas a fining tube, located downstream from the melting vessel 15 andcoupled to the melting vessel 15 by way of a first connecting tube 36. Amixing vessel 42, such as a stir chamber, can also be located downstreamfrom the fining vessel 38. A delivery vessel 46, such as a bowl, may belocated downstream from the mixing vessel 42. As depicted, a secondconnecting tube 40 couples the fining vessel 38 to the mixing vessel 42and a third connecting tube 44 couples the mixing vessel 42 to thedelivery vessel 46. As further illustrated, a downcomer 48 is positionedto deliver glass melt from the delivery vessel 46 to an inlet 50 of aforming vessel 60. In the embodiment schematically depicted in FIG. 1,the melting vessel 15, fining vessel 38, mixing vessel 42, deliveryvessel 46, and forming vessel 60 are examples of various glass meltstations that may be located in series along the glass forming apparatus10.

The melting vessel 15 is typically made from a refractory material, suchas refractory (e.g., ceramic) brick. The glass forming apparatus 10 mayfurther include components that are typically made from platinum orplatinum-containing metals such as platinum-rhodium, platinum-iridiumand combinations thereof, but which may also comprise such refractorymetals such as molybdenum, palladium, rhenium, tantalum, titanium,tungsten, ruthenium, osmium, zirconium, and alloys thereof and/orzirconium dioxide. The platinum-containing components can include one ormore of the first connecting tube 36, the fining vessel 38, the secondconnecting tube 40, the standpipe 30, the mixing vessel 42, the thirdconnecting tube 44, the delivery vessel 46, the downcomer 48 and theinlet 50. The forming vessel 60 can also be made from a refractorymaterial and is designed to form the glass melt into a glass ribbon 12.

FIG. 2 is a cross sectional perspective view of the glass formingapparatus 10 along line 2-2 of FIG. 1. As shown, the forming vessel 60includes a forming wedge 62 comprising a pair of downwardly inclinedforming surface portions 66 a, 66 b that extend between opposed ends 64a, 64 b of the forming wedge 62. The downwardly inclined forming surfaceportions 66 a, 66 b converge along a downstream direction 68 to form aroot 70. A draw plane 72 extends through the root 70. The glass ribbon12 may be drawn in the downstream direction 68 along the draw plane 72.The draw plane 72 bisects the root 70 in a generally horizontal,lengthwise direction of the forming vessel. However, it should beunderstood that the draw plane 72 may extend at other orientations withrespect to the root 70. While FIGS. 1 and 2 generally depict oneembodiment of a glass forming apparatus and a forming vessel, it shouldalso be understood that aspects of the present disclosure may be usedwith various other forming vessel configurations.

Referring to FIGS. 1 and 2, in certain embodiments, the forming vessel60 may comprise an edge director 80 a, 80 b intersecting with the pairof downwardly inclined forming surface portions 66 a, 66 b. The edgedirectors help achieve a desired glass ribbon width and edge beadcharacteristics by directing the molten glass proximate to the root 70of the forming vessel 60. In further embodiments, the edge director canintersect with both downwardly inclined forming surface portions 66 a,66 b. In addition or alternatively, in certain embodiments an edgedirector can be positioned at each of the opposed ends 64 a, 64 b of theforming wedge 62. For instance, as shown in FIG. 1, an edge director 80a, 80 b can be positioned at each of the opposed ends 64 a, 64 b of theforming wedge 62 with each edge director 80 a, 80 b configured tointersect with both of the downwardly inclined forming surface portions66 a, 66 b. As further illustrated, each edge director 80 a, 80 b issubstantially identical to one another. However, it should be understoodthat, in alternative embodiments, the edge directors may have differentconfigurations and/or geometries depending on the specificcharacteristics of the glass forming apparatus. Further, it should beunderstood that various forming wedge and edge director configurationsmay be used in accordance with aspects of the present disclosure. Forexample, aspects of the present disclosure may be used with formingwedges and edge director configurations as disclosed in U.S. Pat. Nos.3,451,798, 3,537,834, 7,409,839 and/or U.S. Provisional Pat. ApplicationNo. 61/155,669, filed Feb. 26, 2009, each of which are hereinincorporated by reference.

Referring now to FIGS. 2 and 3, an embodiment of an edge director thatmay be used with aspects of the present disclosure is schematicallydepicted. The first edge director 80 a will be described in more detail.However, it should be understood that the second edge director 80 b, maybe identical to or of a similar construct as the first edge director 80a. Use of identical edge directors can be beneficial for providing auniform glass ribbon. However, it should be understood that theindividual edge directors may also have different configurations and/orgeometries to accommodate various glass forming apparatus and/or formingvessel configurations.

FIGS. 2 and 3 illustrate a first side of one embodiment of a first edgedirector 80 a positioned with respect to the first downwardly inclinedforming surface portion 66 a of the forming wedge 62. Although notdepicted, the first edge director 80 a further includes a second sidepositioned with respect to the second downwardly inclined formingsurface portion 66 b of the forming wedge 62. The second side of thefirst edge director 80 a is a mirror image of the first side about thedraw plane 72 bisecting the root 70. As depicted, the first side of thefirst edge director 80 a includes a first surface 82 that intersects thefirst downwardly inclined forming surface portion 66 a of the formingwedge 62.

In some embodiments, each opposed end 64 a, 64 b of the forming wedge 62is provided with a retaining block 84 designed to laterally position thecorresponding first and second edge directors 80 a, 80 b. Optionally, asdepicted, the first edge director 80 a can include an upper portion 86and a lower portion 88. The lower portion 88 can, in some embodiments,join the first edge director 80 a on the first opposed end 64 a with thesecond edge director 80 b on the second opposed end 64 b. Joining theedge directors 80 a, 80 b together is beneficial to simplify assembly ofthe edge directors 80 a, 80 b to the forming wedge 62. In furtherembodiments, the upper portions 86 of the edge directors 80 a, 80 b maybe provided separately. For example, as depicted, the first edgedirector 80 a is separate from the second edge director 80 b and theseparate edge directors are assembled independently to each of the pairof downwardly inclined forming surface portions 66 a, 66 b of theforming wedge 62. With certain embodiments, providing upper portions 86that are not joined may simplify manufacture of the edge directors 80 a,80 b.

The glass forming apparatus 10 also includes at least one edge rollerassembly for drawing glass ribbon from the root 70 of the forming vessel60. For example, the apparatus may include a pair of edge rollerassemblies 130 a, 130 b, as depicted in FIG. 1. Referring to FIGS. 1 and2, the edge roller assemblies 130 a, 130 b (edge roller assembly 130 adepicted in FIG. 2) generally include a first pair of edge rollers 132configured to engage a corresponding edge of the glass ribbon as theribbon is drawn from the root 70 of the forming wedge 62. The edgeroller assemblies 130 a, 130 b aid in drawing the glass ribbon 12 fromthe root 70 of the forming wedge 62 and also facilitate proper finishingof the edges of the glass ribbon. For example, the edge rollerassemblies 130 a, 130 b may provide the desired edge characteristics andproper fusion of the edge portions of the molten glass being drawn offopposed surfaces of the edge director 80 a, 80 b associated with thepair of downwardly inclined forming surface portions 66 a, 66 b. Incertain embodiments, the edge roller assembly 130 a, 130 b can belocated at various positions within the viscous region of the glassbeing drawn from the root 70. For instance, in some embodiments the edgeroller assemblies 130 a, 130 b can be located anywhere from immediatelybelow the root 70 to a position about 38.1 centimeters below the root70. However, it should be understood that other positions arecontemplated. For example, the edge roller assemblies 130 a, 130 b canbe located at a position within a range of from about 20 centimeters toabout 25.5 centimeters below the root 70.

As depicted in FIG. 1, in one embodiment, a first edge roller assembly130 a is associated with the first edge director 80 a and a second edgeroller assembly 130 b is associated with the second edge director 80 b.In the embodiments described herein, each edge roller assembly 130 a,130 b is substantially identical to the other.

FIGS. 2 and 3 depict one embodiment of an edge roller assembly 130 a. Asdepicted in FIG. 2, the first edge roller assembly 130 a includes afirst pair of edge rollers 132 including a first edge roller 132 a and asecond edge roller 132 b. The edge rollers 132 a, 132 b are configuredto simultaneously engage the first side and the second side of a glassribbon 12 drawn from the root 70 of the forming wedge 62. The first edgeroller assembly 130 a includes a first shaft 134 a attached to the firstedge roller 132 a and a second shaft 134 b attached to the second edgeroller 132 b. The first and second shafts 134 a, 134 b extend through ahousing seal plate 136 and are rotatably driven by a motor 138. Thehousing seal plate 136 provides a closure to an opening (not shown)leading to an area in which the motor 138 is located. The housing sealplate 136 forms part of housing 14 (FIG. 1) which encloses the formingvessel 60, edge directors 80 a, 80 b and the edge roller assemblies 130a, 130 b. The housing 14 may comprise a refractory material, steel,and/or other thermal insulation to protect sensitive components of themotor and/or other mechanisms located within the housing as well as tothermally insulate the forming vessel 60, and the molten glass flowingin and around the forming vessel 60, from the surrounding environment.

Referring now to FIG. 3, in certain embodiments the first and secondrollers 132 a, 132 b may be actively cooled (e.g., with gas or liquid)to help reduce the likelihood of molten glass being deposited on theedge rollers 132 a, 132 b and adhering thereto. For example, as shown inFIG. 3, an inlet line 152 is configured to extend through each shaft 134a, 134 b to provide a cooling liquid to the first and second rollers 132a, 132 b. An outlet line 154 also extends through each shaft 134 a, 134b to return heated liquid to a fluid source 156. A hydraulic pump 158can draw liquid from the fluid source and pass the liquid through a heatexchanger 160 to remove heat transferred from the first and secondrollers 132 a, 132 b before cycling the liquid back through the inletline 152 to continue cooling the first and second rollers 132 a, 132 b.

For glass forming apparatuses as depicted in FIGS. 1-3, it has beenfound that thermal gradients within the housing 14, such as thermalgradients caused by the localized cooling of the edge roller assemblies130 a, 130 b may cause devitrification of the molten glass flowing overthe edge directors 80 a, 80 b. Specifically, the cooler edge rollers actas a heat sink, drawing heat from the edge directors 80 a, 80 b, therebyreducing the temperature of the edge directors 80 a, 80 b. As the moltenglass drawn over the forming vessel 60 contacts the cooler edgedirectors 80 a, 80 b, the molten glass can devitrify, disrupting theflow of molten glass and potentially introducing defects in the glassribbon drawn from the root 70 of the forming vessel 60.

Referring again to FIG. 1, to prevent the devitrification of the moltenglass in contact with the edge directors 80 a, 80 b, the glass formingapparatus 10 further includes a replaceable heating cartridge 110 a, 110b positioned in the housing 14. The replaceable heating cartridge may beconfigured to direct heat onto the edge directors 80 a, 80 b, therebymaintaining the edge directors 80 a, 80 b at a temperature above thedivitrification temperature of the molten glass, thereby mitigating thedevitrification of the glass. The replaceable heating cartridge 110 a,110 b may also serve as a barrier to thermally isolate and shield theedge directors 80 a, 80 b from the cooler edge rollers 132 a, 132 b,thereby preventing heat transfer from the edge directors to the edgerollers 132 a, 132 b. For example, the glass forming apparatus 10 mayinclude one or more replaceable heating cartridges 110 a, 110 b (onedepicted) that are removably mounted in the housing 14 of the glassforming apparatus 10. The replaceable heating cartridges can be replacedor upgraded during a draw campaign rather than waiting until the end ofthe campaign, thereby reducing production losses and equipment downtime.FIGS. 1-5 schematically depict embodiments of replaceable heatingcartridges 110 a, 110 b inserted in the housing 14 of the glass formingapparatus 10.

Referring now to FIGS. 3-5, in one embodiment, the first replaceableheating cartridge 110 a includes an enclosure 120 having a heatdirecting surface 122 with at least one heating element 124 positionedon or adjacent to the face thereof. The enclosure 120 may be fabricatedfrom a variety of materials that absorb or, reflect heat energy, or thatprovide a thermal shield while maintaining structural integrity undertypical temperature conditions associated with the glass formingapparatus 10. For instance, the enclosure 120, and other portions of thereplaceable heating cartridge 110 a, can be formed from a refractorymaterial, high temperature, nickel-based alloys, steel (e.g., stainlesssteel), or other alloys or other materials or combinations of materials,to meet the structural and/or thermal requirements of the glass formingapparatus 10. For example, in one embodiment, the enclosure 120 may bemade of nickel-based alloys, such as Hanes 214. In one particularembodiment, the heat directing surface 122 of the first replaceableheating cartridge 110 a is formed from a ceramic refractory backermaterial with low emissivity. Suitable ceramic refractory materialsinclude, without limitation, SALI board available from Zircar ceramics.Portions of the enclosure which are not directly exposed to the hightemperatures of the glass forming apparatus 10 may be made frommaterials suitable for lower temperature applications. For example, theback face 125 of the enclosure 120 may be made from stainless steel,such as, for example, 420 stainless steel.

According to certain embodiments, the heat directing surface 122 of thereplaceable heating cartridge 110 a is typically inclined at an angle αof less than about 90° with respect to a bottom surface 126 of theenclosure 120. In certain embodiments, the inclined angle α of the heatdirecting surface 122 is from about 45° to about 75° relative to thebottom surface 126 of the enclosure. In specific embodiments, theinclined angle α of the heat directing surface 122 is about 60° relativeto the bottom surface 126. The inclined angle of the heat directingsurface 122 facilitates positioning the first replaceable heatingcartridge 110 a in the housing 14 of the glass forming apparatus suchthat the heat directing surface 122 faces the first edge director 80 a.The angle of the heat directing surface 122 and the orientation of thefirst replaceable heating cartridge 110 a enables the heat directingsurface 122 to radiate and direct heat toward and onto the first edgedirector 80 a with only minimal loss of heat to the surroundingenvironment. In addition, the angle of the heat directing surface 122and the position of the replaceable heating cartridge 110 a is such thatthe view factor from the heat directing surface is greater at the firstedge director 80 a than at the first pair of edge rollers 132 a. Theterm “view factor,” as used herein, refers to the relative proportion ofthermal radiation from the heat directing surface 122 which is incidenton the specified surface (i.e., either the edge director 80 a or theedge rollers 132 a, 132 b).

In some embodiments, the replaceable heating cartridge 110 a mayoptionally include a shield member 121 extending from the center facet162 of the heat directing surface 122 proximate the bottom surface 126of the replaceable heating cartridge 110 a, as schematically depicted inFIG. 4A. The shield member 121 may provide additional thermal shieldingand reduce heat loss from the first edge director 80 a to theenvironment below the replaceable heating cartridge 110 a.

Still referring to FIGS. 3-5, the replaceable heating cartridge 110 aalso includes a heating element 124 positioned on or adjacent to theheat directing surface 122 of the enclosure 120. In certain embodiments,the heating element 124 positioned on or adjacent to the heat directingsurface 122 is a resistance heating element. The material of theresistance heating element can be molybdenum disilicide, platinum,platinum-rhodium, iron-chromium-aluminum alloys such as Kanthal Al,Kanthal APM (a ferritic iron-chromium-aluminum alloy), or anotherappropriate winding material.

In some embodiments, the heating element 124 may be constructed fromwire formed from one of the above referenced materials which is woundinto a coil. For example and without limitation, in one embodiment, theheating element 124 may be constructed from platinum wire having acircular cross section which is wound around a mandrel having a circularcross section in order to form a coil with a circular cross section.However, it should be understood that other cross sectional shapes ofthe coil are possible and contemplated. For example, in one embodiment,wire of the heating element may be wound around a mandrel having anelongated cross section, such as an oval, ellipse, or the like, in orderto produce a coil having the same elongated cross section as themandrel. It has been determined that forming the heating element 124from a coil with an elongated cross section may improve the heatingefficiency of the coil by increasing the power-carrying capacity of thecoil. For example, it has been determined that platinum wire having acircular cross section which is wound into an oval coil with a ⅜″ (9.53mm) internal major diameter and a 3/16″ (4.78 mm) internal minordiameter has a 25% increase in power carrying capacity compared to around coil having a ⅜″ (9.53 mm) diameter formed from the same platinumwire. The increased power carrying capacity translates to improvedheating efficiency and efficacy for the coil.

Still referring to FIGS. 3-5, located behind the face of the heatdirecting surface 122 and within the enclosure 120 are one or moreblocks of refractory material 128 which insulate the heat directingsurface 122 from the balance of the replaceable heating cartridge 110 a.In certain embodiments. The refractory blocks 128 are oriented inalternating vertical stacks and horizontal stacks, as depicted in FIG.4B, to minimize heat transfer from the heat directing surface 122.Specifically, it is believed that alternating vertical stacks andhorizontal stacks of refractory blocks 128 may assist in reducing heatat seams between the blocks. In embodiments, the refractory material 128can be oriented at an angle approximately equal to the angle of the heatdirecting surface 122. In still other embodiments, such as where theheat directing surface 122 is formed from a refractory material such asSALI board or the like, the refractory material of the heat directingsurface 122 may extend into the enclosure. In the embodiments describedherein, the refractory blocks 128 may be formed from commerciallyavailable refractory materials including, without limitation, DuraBoard®3000 and/or DuraBoard® 2600.

In certain embodiments, as shown in FIGS. 4 and 5, the heat directingsurface 122 comprises a plurality of facets 161 orientated to at leastpartially surround the edge director(s). For example, in the embodimentof the replaceable heating cartridge 110 a schematically depicted inFIGS. 4 and 5, the heat directing surface 122 has a center facet 162 andtwo side facets 164 on opposite ends of the center facet 162. Typically,the largest angle β between each of the two side facets 164 relative tothe center facet 162 is from about 145° to about 175°. For example, thelargest angle β between each of the two side facets 164 relative to thecenter facet 162 may about 160°, although it should be understood thatother angles are possible and contemplated.

While the embodiment of the replaceable heating cartridge 110 a depictedin FIGS. 4A, 4B and 5 comprises a heat directing surface 122 withmultiple facets, it should be understood that other embodiments arecontemplated. For example, the heat directing surface 122 may comprise acurved surface. In the embodiment of the replaceable heating cartridge110 a depicted in FIG. 6, for example, the heat directing surface 122comprises a frusto-conical 166 design. The faceted 161 or frusto-conical166 design of the heat directing surface 122 increases the amount ofheat directed toward the first edge director 80 a, thereby minimizingheat loss to the surrounding environment and generally improving theheating efficiency of the replaceable heating cartridge with respect tothe edge director. In addition, the frusto-conical and/or faceteddesigns of the heat directing surface 122 also improve the view factorbetween the heat directing surface 122 and the first edge director 80 a.

Referring again to FIGS. 1 and 3, in the embodiments described herein,the replaceable heating cartridges 110 a, 110 b are positioned in thehousing 14 of the glass forming apparatus 10 such that the lower edge123 of the heat directing surface 122 and the bottom surface 126 of theenclosure 120 are at least partially positioned between the edgedirectors 80 a, 80 b and the plurality of edge rollers 132 to thermallyshield the edge directors 80 a, 80 b from the plurality of edge rollers132. As shown in FIG. 1, a first replaceable heating cartridge 110 a isassociated with the first edge director 80 a. Likewise, a secondreplaceable heating cartridge 110 b is associated with the second edgedirector 80 b. In the embodiments described herein, it should beunderstood that the replaceable heating cartridge can function as both aheater for heating the corresponding edge director as well as a thermalshield for thermally isolating the edge director and the plurality ofedge rollers from one another. This dual-functionality is enabled by theangled heat directing surface 122 of the replaceable heating cartridgewhich permits the replaceable heating cartridge to be at least partiallypositioned between the edge director and the plurality of edge rollerswithout contacting or otherwise interfering with the operation of eithercomponent. As such, the replaceable heating cartridges are configured toreduce heat loss from the corresponding edge directors 80 a, 80 b tonon-target areas, and in particular, heat loss to the cooled edge rollerassemblies 130 a, 130 b. Such non-target areas can include nearby areasof the glass making apparatus and/or other locations capable of drawingor sinking heat from the edge directors 80 a, 80 b.

Referring now to FIG. 3, a variety of attachment structures may be usedto mount the replaceable heating cartridge 110 a with respect to theedge director 80 a. For example, in the embodiment shown in FIG. 3, thereplaceable heating cartridge 110 a is mounted in a port of the housingseal plate 136 such that the replaceable heating cartridge 110 a ispositioned below the forming vessel 60 between the edge director 80 aand the first pair of edge rollers 132, as described above. In thisembodiment, the replaceable heating cartridge 110 a may be mounted on abracket 114 engaged with the housing 14 and/or the housing seal plate136. Additionally or alternatively, the replaceable heating cartridge110 a can rest on T-wall support brackets 112 that are attached to thehousing seal plate 136. In some embodiments, the replaceable heatingcartridge may be adjustably mounted relative to the edge director bybeing mounted to the movable housing seal plate 136.

In certain embodiments, the first replaceable heating cartridge 110 acan be positioned below a portion of the first edge director 80 a, andextends generally in a length-wise direction relative to the lengthdimension of the forming wedge 62 and in close proximity to the shafts134 a, 134 b. As shown in FIGS. 2 and 3, the first replaceable heatingcartridge 110 a may be positioned below only a portion of the first edgedirector 80 a. Indeed, as shown in FIG. 3, the first replaceable heatingcartridge 110 a is positioned such that the lower edge 123 of the heatdirecting surface 122 and the bottom surface 126 terminates outside ofthe corresponding edge 13 of the glass ribbon 12. As such, the loweredge 123 of the heat directing surface 122 and the bottom surface 126 ofthe first replaceable heating cartridge 110 a only extend under anoutside portion 83 of the first edge director 80 a without extendingunder an inner portion 85 of the first edge director. In certainembodiments the lower edge 123 of the heat directing surface 122 and thebottom surface 126 of the first replaceable heating cartridge 110 a donot extend inward in a direction toward the flow of molten glass beyondthe width-wise extent of the root. That is, the lower edge 123 of theheat directing surface 122 and the bottom surface 126 of the firstreplaceable heating cartridge 110 a are not directly beneath the root.Referring to FIG. 3 and FIG. 4A, in other embodiments, the replaceableheating cartridge 110 is positioned below the edge director such thatthe lower edge 123 of the center facet 162 of the heat directing surface122 does not extend beyond the position of the dam 81 of the formingwedge 62 (e.g., the intersection of the forming wedge 62 with theretaining block 84) at the level of the root 70. That is, the lower edge123 of the center facet 162 does not extend under the edge director 80 apast a vertical line drawn from the forming wedge 62 at the intersectionof the root 70 of the forming wedge 62 with the dam 81 of the formingwedge 62. Positioning the replaceable heating cartridge 110 a in thismanner maximizes the heat directed onto the edge director while ensuringthat the lower edge 123 of the center facet 162 of the heat directingsurface 122 does not interfere with the glass ribbon 12 drawn from theforming wedge 62. Accordingly, it should be understood that the angledheat directing surface 122 of the replaceable heating cartridge 110 a isoriented to effectively direct heat onto the inner portion 85 of thefirst edge director 80 a, thereby increasing the temperature of theinner portion 85 of the first edge director 80 a and mitigating thedevitrification of molten glass with this portion of the edge director80 a. Providing the first replaceable heating cartridge 110 a at alocation underneath only a portion of the first edge director 80 a inthis manner, or in certain other embodiments not extending beneath theroot, can provide sufficient reduction of heat loss to non-target areaswhile avoiding possible interference with the molten glass being drawnfrom the root 70 of the forming wedge 62.

In addition or alternatively, the first replaceable heating cartridge110 a can be positioned partially or entirely downstream from the firstedge director. For instance, as shown in FIGS. 2 and 3, the firstreplaceable heating cartridge 110 a is depicted as being positionedentirely downstream along downstream direction 68 from the first edgedirector 80 a. Positioning the first replaceable heating cartridge 110 aentirely downstream of the first edge director 80 a helps minimize heatloss from the first edge director 80 a to non-target areas locateddownstream from the first edge director 80 a.

In alternative embodiments (not shown), the first replaceable heatingcartridge 110 a can be positioned partially downstream from the firstedge director 80 a. For example, the first replaceable heating cartridge110 a can be positioned downstream from an upper portion of the firstedge director 80 a while a lower portion of the first edge director 80 ais positioned downstream from the first replaceable heating cartridge110 a. In additional embodiments, the first replaceable heatingcartridge 110 a may be positioned adjacent to a first side of the firstedge director 80 a with an upper portion of the first edge director 80 aextending above the first replaceable heating cartridge 110 a and alower portion of the first edge director 80 a extending below the firstreplaceable heating cartridge 110 a. Positioning the first replaceableheating cartridge 110 a only partially downstream from the first edgedirector 80 a may provide sufficient reduction of heat loss tonon-target areas while providing a compact design or otherwiseaccommodating different forming vessel designs.

As shown in FIGS. 2 and 3, in certain embodiments the first replaceableheating cartridge 110 a may be positioned partially between the firstpair of edge rollers 132 and the first edge director 80 a. For example,as shown in FIG. 3, the lower edge 123 of the heat directing surface 122and a bottom surface 126 of the first replaceable heat cartridge 110 aonly extend between the outside portion 83 of the first edge director 80a and the first shaft 134 a and the second shaft 134 b of the first pairof edge rollers 132. The lower edge 123 of the heat directing surface122 and a bottom surface 126 of the first replaceable heat cartridge 110a terminates outside of the corresponding edge 13 of the glass ribbon12. As such, the lower edge 123 of the heat directing surface 122 and abottom surface 126 of the first replaceable heat cartridge 110 a do notextend between the inner portion 85 of the first edge director 80 a andthe edge rollers 132 a, 132 b of the first pair of edge rollers 132.However, the angled heat directing surface 122 of the replaceableheating cartridge 110 a is oriented to effectively direct heat onto theinner portion 85 of the first edge director 80 a, thereby increasing thetemperature of the inner portion 85 of the first edge director 80 a andmitigating the devitrification of molten glass with this portion of theedge director 80 a.

In certain embodiments, the glass forming apparatus 10 can also includeone or more optional additional heaters associated with one or both ofthe edge directors 80 a, 80 b. If provided, the one or more heaters canbe constructed with various configurations that are capable of heatingan interface between the molten glass and the edge directors 80 a, 80 b.For example, refractory or metallic resistance heaters, inductionheaters or other heating devices may be used. In certain embodiments,resistive heaters (e.g., platinum winding, molybdenum disilicidewinding, etc.) may be used. These heaters can be positioned at variouslocations within the housing 14 with respect to the corresponding edgedirector. As shown in FIG. 3, in one embodiment a heating device 170 amay be positioned adjacent to the first edge director 80 a, above thereplaceable heating cartridge 110 a. In this embodiment, the heatingdevice 170 a is oriented to radiate heat laterally toward the first edgedirector 80 a. In addition or alternatively, a second heating device 170b may be positioned inside the first edge director 80 a and configuredto internally heat the first edge director 80 a. Additional heatingdevices may be used at different locations to further heat the edgedirector. In embodiments, these devices may be formed from coils havingelongated cross sections in order to improve the heating efficacy of thecoils with respect to the edge directors. In the illustratedembodiments, the additional heating devices 170 a, 170 b are positionedupstream from the replaceable heating cartridge 110 a. However, itshould be understood that, in other embodiments the heaters may belocated in other positions, including downstream of the replaceableheating cartridge 110 a.

As further illustrated in FIG. 3, in certain embodiments the apparatusmay further include a controller 180 configured to control heatingassociated with the first replaceable heat cartridge 110 a. In certainembodiments the controller 180 may be operably connected to the firstreplaceable heating cartridges 110 a and also to one or more optionalheaters (e.g., heating devices 170 a, 170 b) associated with the edgedirector 80 a. The controller 180 may include a processor and memorystoring computer readable and executable instructions which, whenexecuted by the processor, regulates the power to the replaceableheating cartridge and/or the heating devices, thereby increasing ordecreasing the heat provided by the replaceable heating cartridge and/orthe heating devices based on feedback or other process parameters.

In certain embodiments, the controller can be configured to operate thefirst replaceable heating cartridge 110 a and the one or more optionalheating devices 170 a, 170 b based on thermal feedback from the glassforming apparatus. For example, in one embodiment the controller 180 isconfigured to obtain thermal feedback from a thermal sensor 182. Thefeedback obtained by the thermal sensor 182 can be used by thecontroller 180 to adjust the replaceable heating cartridge and/or theheating devices in order to provide managed control of a thermalcharacteristic of the apparatus as the manufacture of glass ribbonproceeds. The thermal characteristic can include, for example, thetemperature and/or heat loss associated with: a portion of the glassforming apparatus, such as the heat directing surface 122 of thereplaceable heating cartridges 110 a, 110 b; a portion of the edgedirectors 80 a, 80 b; a portion of the end of the forming vessel 60;portions of the molten glass; and/or other features of the glass formingapparatus 10.

In one embodiment, the thermal sensor 182 may detect a temperature abovea target level and the controller 180 may reduce power to the firstreplaceable heating cartridge 110 a such that less heat is transferredto the target area, thereby reducing the temperature until the targetlevel temperature is obtained. Alternatively, in certain embodiments thethermal sensor 182 may detect a temperature below a target level,wherein the controller 180 may increase power to the replaceable heatingcartridge, such that more heat is transferred to the target area,thereby increasing the temperature until the target level temperature isobtained.

Various methods of making glass can incorporate various features of theglass forming apparatus 10 described above. In one embodiment, batchmaterial can be converted to molten glass received by the forming vessel60 by way of the exemplary series of glass melt stations describedabove. As shown in FIG. 2, the method includes the step of flowingmolten glass 17 over the pair of downwardly inclined forming surfaceportions 66 a, 66 b of the forming wedge 62. As shown in FIGS. 2 and 3,the method further includes the steps of flowing molten glass over theedge director and drawing the molten glass from the root 70 of theforming wedge 62 to form the glass ribbon 12. The method also includesthe step of providing a pair of edge rollers that are configured toengage the edge of the glass ribbon. The edge rollers are rotated by themotor 138 to draw the glass ribbon 12 from the root 70 of the formingwedge 62. As further illustrated, the method also includes the step ofheating the edge directors with replaceable heating cartridges 110 a,110 b to reduce heat loss from the corresponding edge directors 80 a, 80b to non-target areas, and in particular, heat loss to the cooled edgerollers, as described above. It will be appreciated that aspects of thedisclosure may positively impact glass edge quality and preventdegradation of edge conditions due to devitrification and crystal growththat may otherwise occur on the edge director surfaces.

EXAMPLES

The embodiments described herein will be further clarified by thefollowing examples.

Example 1

A computational model was developed to compare the surface temperatureof an edge director heated with a heater having a conventional design tothe surface temperature of an edge director heated with a replaceableheating cartridge as described herein. The conventional heater wasmodeled with a heat directing surface with an inclined angle α of 90°relative to the base of the heater. The conventional heater was modeledwith platinum alloy heating elements disposed on the heat directingface. The replaceable heating cartridge was modeled with a heatdirecting surface having an inclined angle α of 60° relative to the baseof the replaceable heating cartridge. The replaceable heating cartridgewas modeled with molybdenum disilicide heating elements positioned onthe heat directing face. Both the conventional heater and thereplaceable heating cartridge were modeled at an operating power of 6900W.

FIG. 7 graphically depicts the normalized temperature differential onthe surface of the edge director due to heating with the replaceableheating cartridge having an inclined angle α of 60° relative to theconventional heater with an inclined angle α of 90°. That is, theisotherms of FIG. 7 show the increase in the surface temperature of theedge director as a result of heating with a heating cartridge having aninclined angle α of 60° relative to heating with a conventional heaterwith an inclined angle α of 90°. As depicted in FIG. 7, the replaceableheating cartridge with an inclined angle α of 60° increased the averagetemperature of the edge director by about 18° C. (averaged over theentire surface of the edge director) relative to the conventional designwith an inclined angle α of 90°. Regardless of the heater used, thelowest temperature of the edge director generally occurs at the outercorner of the edge director at the root elevation, both of which arelabeled in FIG. 7. However, the modeled date demonstrates that thereplaceable heating cartridge with an inclined angle α of 60° increasedthe temperature of this outer corner by about 19° C. relative to theconventional design with an inclined angle α of 90°.

The data of FIG. 7 indicates that the replaceable heating cartridgesdescribed herein which have heat directing surfaces having an inclinedangle α of less than 90°, such as from about 45° to about 75°, are moreeffective at maintaining the surface of the edge director at an elevatedtemperature relative to conventional heaters (i.e., heaters with aninclined angle α of) 90° and, as such, are more effective at reducingthe devitrification of glass drawn over the edge director. Inparticular, the inclined angle of the heat directing surface allows heatto be more efficiently radiated towards the edge director. In addition,the inclined angle of the heating surface allows for the removableheating cartridge to be inserted between the pulling rolls and the edgedirector thereby thermally shielding the edge director from the pullingrolls which act as a heat sink.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the embodiments describedherein without departing from the spirit and scope of the claimedsubject matter. Thus it is intended that the specification cover themodifications and variations of the various embodiments described hereinprovided such modification and variations come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method of making a glass ribbon comprising:flowing molten glass over a pair of downwardly inclined forming surfaceportions of a forming wedge, the pair of downwardly inclined formingsurface portions converging along a downstream direction to form a root;flowing the molten glass over an edge director intersecting with atleast one of the pair of downwardly inclined forming surface portions;drawing the molten glass from the root of the forming wedge to form theglass ribbon; engaging an edge portion of the glass ribbon with aplurality of edge rollers positioned downstream from the root and theedge director, the plurality of edge rollers extending through ahousing; heating the edge director with a replaceable heating cartridgelocated in a port in the housing, wherein the replaceable heatingcartridge is positioned between the plurality of edge rollers and theedge director, the replaceable heating cartridge comprising an enclosurehaving a heat directing surface that is inclined at an angle of lessthan about 90° with respect to a bottom surface of the enclosure, theheat directing surface comprising at least one heating elementpositioned on or adjacent to a face thereof, wherein the replaceableheating cartridge is oriented such that the heat directing surface facesthe edge director, a view factor from the heat directing surface isgreater at the edge director than at the plurality of edge rollers, anda lower edge of the heat directing surface and the bottom surface of thereplaceable heating cartridge are at least partially positioned betweenthe edge director and the plurality of edge rollers to thermally shieldthe edge director from the plurality of edge rollers; and detecting atemperature of a predetermined target area and adjusting the replaceableheating cartridge such that more or less heat is transferred from thereplaceable heating cartridge to the predetermined target area, therebyvarying the temperature of the predetermined target area until a targetlevel temperature is obtained.
 2. The method of claim 1, wherein theangle of the heat directing surface is from about 45° to about 75°relative to the bottom surface.
 3. The method of claim 1, wherein theheat directing surface comprises a plurality of facets orientated to atleast partially surround the edge director.
 4. The method of claim 3,wherein the plurality of facets comprises a center facet and two sidefacets on opposite ends of the center facet, wherein a largest anglebetween each of the two side facets relative to the center facet is fromabout 145° to about 175°.
 5. The method of claim 1, wherein the heatdirecting surface comprises a curved surface such that the heatdirecting surface at least partially surrounds the edge director.
 6. Themethod of claim 1, wherein the replaceable heating cartridge isreplaceable as the glass ribbon is being formed.
 7. The method of claim1, wherein the predetermined target area comprises at least one of theheat directing surface, the edge director, the forming wedge and themolten glass.
 8. The method according to claim 1, wherein the adjustingcomprises controlling electrical power to the replaceable heatingcartridge with a controller operably connected to the replaceableheating cartridge and configured to receive thermal feedback from athermal sensor.